The present disclosure relates to a method and apparatus for evacuating a chamber using a vacuum pump and booster.
Vacuum pumps are used or needed in many industrial applications, such as power generation, steel manufacturing, and in the semiconductor, solar and flat panel display (FPD) industries, for instance. It is to be noted that the present invention is not limited to any one of these industrial applications. However, for convenience, the present invention is described below with reference to the semiconductor, solar, LED (light emitting diode) and FPD manufacturing industries (collectively referred to as semiconductor manufacturing). Of course, the skilled person understands that other industrial processes or applications can equally benefit from using the present invention.
Vacuum pumps are generally designed to run at an optimal speed during normal use. A vacuum pump's efficiency can be improved by using the pump in conjunction with a booster pump. With reference to FIG. 1 (in which a known semiconductor processing unit 1 is shown), the booster pump 28 is disposed between the vacuum pump 30 and a chamber being evacuated by the vacuum pump, which together makes up a vacuum pumping system. The booster is arranged to increase the flow rate of gas from the chamber. Typically, the booster is configured as a single stage roots blower and it does not significantly compress the gas. The booster/dry vacuum pump combination can remove relatively large volumes of gas from the chamber to evacuate it to pressure levels in the medium vacuum range.
In semiconductor manufacturing, substrates are processed in a process chamber 2 which is held at vacuum to enable deposition of material onto the substrate to occur. On a given tool, there might be a number of processing chambers accessible from a transfer chamber 4, also held at vacuum. Depending on the process, the substrates typically comprise a silicon wafer or a glass panel. It is common to use an airlock or loadlock chamber 10 to isolate the process chambers and transfer chamber from atmospheric pressure and to enable substrates to be moved to and from the process chamber without significant loss of vacuum pressure within the process chamber or transfer chamber. In this way, efficient movement of wafers or glass substrates into the main processing chamber of a production tool is enabled.
Typically the loadlock chamber has two sealed doors—a first door 12 is used to isolate the loadlock from a room at atmospheric pressure and a second door 14 is used to isolate the production tool from the loadlock. During normal use, it is not possible to open both the first and second doors at the same time. Opening the first door enables a batch of substrates to be placed in the loadlock. At this point the loadlock chamber is at atmospheric pressure and is isolated from the process chamber. The first door is then closed to isolate the loadlock chamber from the room and the process chamber. A vacuum pumping system 20 is used to evacuate the loadlock chamber before the second door is opened and the wafer is passed through to the processing chamber. Thus, the processing chamber and process tool are kept at vacuum pressures during the loading and extraction of substrates to or from the tool. Another tool architecture could be ‘inline’, where substrates enter the system through an entry load lock, then move into a connected process chamber, and once the process has completed, continue into an exit load lock at the other end of the machine.
The time taken to evacuate a loadlock chamber can be limiting factor on the amount of substrates being processed by a tool in any given time period. In addition, there is a trend to increase the size of substrates being processed in the processing tool, which is leading to an increase in volume of the associated loadlock chamber. This is particularly the case in solar panel manufacturing (which now requires large area solar panels to be processed onto large glass substrates) and silicon chip processing where wafer size is increasing from 300 mm to 450 mm. It is desirable, therefore, to increase the evacuation rate of loadlock chambers.
The loadlock chamber typically has a dedicated evacuation system 20 comprising one or more vacuum pumps. The process chamber typically uses a different evacuation system 21. This is desirable because of the harsh or corrosive nature of the chemicals used in processing devices within the chamber and the deleterious effect such chemicals have on the pumps evacuating the processing tool. In other words, the loadlock pumps typically do not need to be resistant to harsh chemical or corrosive environments.
The flow of gas from the loadlock chamber 10 to its vacuum pumping system 20 is controlled by a valve 24. When the valve is closed the vacuum pump evacuates any connecting pipes 25 between the loadlock chamber and the pump up to the point of the valve. When the valve opens, the vacuum pump is exposed to a rapid increase of pressure at the pumping system's inlet. This sudden increase in pressure can be many orders of magnitude and can occur within a few micro seconds of the valve opening. As a result, the vacuum pumping system experiences a rapid increase in gas load which can cause deceleration of the booster pump's moving parts thereby causing high noise levels as the pumps compresses relatively high pressure gas at a fast rate. In an evacuation system fitted with a mechanical booster pump 28, such as a roots blower, the sudden increase in inlet pressure causes the booster pump to decelerate very rapidly and generate extremely high noise levels.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.